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Date: Tue, 28 Jul 2020 18:20:33 +0100
From: Tom Parkin <tparkin@...alix.com>
To: netdev@...r.kernel.org
Cc: jchapman@...alix.com, Tom Parkin <tparkin@...alix.com>
Subject: [PATCH 6/6] l2tp: improve API documentation in l2tp_core.h
* Improve the description of the key l2tp subsystem data structures.
* Add high-level description of the main APIs for interacting with l2tp
core.
* Add documentation for the l2tp netlink session command callbacks.
* Document the session pseudowire callbacks.
Signed-off-by: Tom Parkin <tparkin@...alix.com>
---
net/l2tp/l2tp_core.h | 86 ++++++++++++++++++++++++++++++++++++--------
1 file changed, 72 insertions(+), 14 deletions(-)
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 3dfd3ddd28fd..3468d6b177a0 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -15,15 +15,15 @@
#include <net/xfrm.h>
#endif
-/* Just some random numbers */
+/* Random numbers used for internal consistency checks of tunnel and session structures */
#define L2TP_TUNNEL_MAGIC 0x42114DDA
#define L2TP_SESSION_MAGIC 0x0C04EB7D
-/* Per tunnel, session hash table size */
+/* Per tunnel session hash table size */
#define L2TP_HASH_BITS 4
#define L2TP_HASH_SIZE BIT(L2TP_HASH_BITS)
-/* System-wide, session hash table size */
+/* System-wide session hash table size */
#define L2TP_HASH_BITS_2 8
#define L2TP_HASH_SIZE_2 BIT(L2TP_HASH_BITS_2)
@@ -43,9 +43,7 @@ struct l2tp_stats {
struct l2tp_tunnel;
-/* Describes a session. Contains information to determine incoming
- * packets and transmit outgoing ones.
- */
+/* L2TP session configuration */
struct l2tp_session_cfg {
enum l2tp_pwtype pw_type;
unsigned int recv_seq:1; /* expect receive packets with sequence numbers? */
@@ -63,6 +61,11 @@ struct l2tp_session_cfg {
char *ifname;
};
+/* Represents a session (pseudowire) instance.
+ * Tracks runtime state including cookies, dataplane packet sequencing, and IO statistics.
+ * Is linked into a per-tunnel session hashlist; and in the case of an L2TPv3 session into
+ * an additional per-net ("global") hashlist.
+ */
struct l2tp_session {
int magic; /* should be L2TP_SESSION_MAGIC */
long dead;
@@ -101,15 +104,32 @@ struct l2tp_session {
struct l2tp_stats stats;
struct hlist_node global_hlist; /* global hash list node */
+ /* Session receive handler for data packets.
+ * Each pseudowire implementation should implement this callback in order to
+ * handle incoming packets. Packets are passed to the pseudowire handler after
+ * reordering, if data sequence numbers are enabled for the session.
+ */
void (*recv_skb)(struct l2tp_session *session, struct sk_buff *skb, int data_len);
+
+ /* Session close handler.
+ * Each pseudowire implementation may implement this callback in order to carry
+ * out pseudowire-specific shutdown actions.
+ * The callback is called by core after unhashing the session and purging its
+ * reorder queue.
+ */
void (*session_close)(struct l2tp_session *session);
+
+ /* Session show handler.
+ * Pseudowire-specific implementation of debugfs session rendering.
+ * The callback is called by l2tp_debugfs.c after rendering core session
+ * information.
+ */
void (*show)(struct seq_file *m, void *priv);
+
u8 priv[]; /* private data */
};
-/* Describes the tunnel. It contains info to track all the associated
- * sessions so incoming packets can be sorted out
- */
+/* L2TP tunnel configuration */
struct l2tp_tunnel_cfg {
int debug; /* bitmask of debug message categories */
enum l2tp_encap_type encap;
@@ -128,6 +148,12 @@ struct l2tp_tunnel_cfg {
udp6_zero_rx_checksums:1;
};
+/* Represents a tunnel instance.
+ * Tracks runtime state including IO statistics.
+ * Holds the tunnel socket (either passed from userspace or directly created by the kernel).
+ * Maintains a hashlist of sessions belonging to the tunnel instance.
+ * Is linked into a per-net list of tunnels.
+ */
struct l2tp_tunnel {
int magic; /* Should be L2TP_TUNNEL_MAGIC */
@@ -162,10 +188,23 @@ struct l2tp_tunnel {
struct work_struct del_work;
};
+/* Pseudowire ops callbacks for use with the l2tp genetlink interface */
struct l2tp_nl_cmd_ops {
+ /* The pseudowire session create callback is responsible for creating a session
+ * instance for a specific pseudowire type.
+ * It must call l2tp_session_create and l2tp_session_register to register the
+ * session instance, as well as carry out any pseudowire-specific initialisation.
+ * It must return >= 0 on success, or an appropriate negative errno value on failure.
+ */
int (*session_create)(struct net *net, struct l2tp_tunnel *tunnel,
u32 session_id, u32 peer_session_id,
struct l2tp_session_cfg *cfg);
+
+ /* The pseudowire session delete callback is responsible for initiating the deletion
+ * of a session instance.
+ * It must call l2tp_session_delete, as well as carry out any pseudowire-specific
+ * teardown actions.
+ */
void (*session_delete)(struct l2tp_session *session);
};
@@ -174,11 +213,16 @@ static inline void *l2tp_session_priv(struct l2tp_session *session)
return &session->priv[0];
}
+/* Tunnel and session refcounts */
void l2tp_tunnel_inc_refcount(struct l2tp_tunnel *tunnel);
void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel);
void l2tp_session_inc_refcount(struct l2tp_session *session);
void l2tp_session_dec_refcount(struct l2tp_session *session);
+/* Tunnel and session lookup.
+ * These functions take a reference on the instances they return, so
+ * the caller must ensure that the reference is dropped appropriately.
+ */
struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);
struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth);
struct l2tp_session *l2tp_tunnel_get_session(struct l2tp_tunnel *tunnel,
@@ -189,33 +233,47 @@ struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth);
struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
const char *ifname);
+/* Tunnel and session lifetime management.
+ * Creation of a new instance is a two-step process: create, then register.
+ * Destruction is triggered using the *_delete functions, and completes asynchronously.
+ */
int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id,
u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
struct l2tp_tunnel **tunnelp);
int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
struct l2tp_tunnel_cfg *cfg);
-
void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);
+
struct l2tp_session *l2tp_session_create(int priv_size,
struct l2tp_tunnel *tunnel,
u32 session_id, u32 peer_session_id,
struct l2tp_session_cfg *cfg);
int l2tp_session_register(struct l2tp_session *session,
struct l2tp_tunnel *tunnel);
-
void l2tp_session_delete(struct l2tp_session *session);
+
+/* Receive path helpers. If data sequencing is enabled for the session these
+ * functions handle queuing and reordering prior to passing packets to the
+ * pseudowire code to be passed to userspace.
+ */
void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
unsigned char *ptr, unsigned char *optr, u16 hdrflags,
int length);
int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb);
-void l2tp_session_set_header_len(struct l2tp_session *session, int version);
+/* Transmit path helpers for sending packets over the tunnel socket. */
+void l2tp_session_set_header_len(struct l2tp_session *session, int version);
int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb,
int hdr_len);
-int l2tp_nl_register_ops(enum l2tp_pwtype pw_type,
- const struct l2tp_nl_cmd_ops *ops);
+/* Pseudowire management.
+ * Pseudowires should register with l2tp core on module init, and unregister
+ * on module exit.
+ */
+int l2tp_nl_register_ops(enum l2tp_pwtype pw_type, const struct l2tp_nl_cmd_ops *ops);
void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);
+
+/* IOCTL helper for IP encap modules. */
int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);
static inline int l2tp_get_l2specific_len(struct l2tp_session *session)
--
2.17.1
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